(function(global, module) {

    var exports = module.exports;

    /**
     * Exports.
     */

    module.exports = expect;
    expect.Assertion = Assertion;

    /**
     * Exports version.
     */

    expect.version = '0.3.1';

    /**
     * Possible assertion flags.
     */

    var flags = {
        not: ['to', 'be', 'have', 'include', 'only']
        , to: ['be', 'have', 'include', 'only', 'not']
        , only: ['have']
        , have: ['own']
        , be: ['an']
    };

    function expect(obj) {
        return new Assertion(obj);
    }

    /**
     * Constructor
     *
     * @api private
     */

    function Assertion(obj, flag, parent) {
        this.obj = obj;
        this.flags = {};

        if (undefined != parent) {
            this.flags[flag] = true;

            for (var i in parent.flags) {
                if (parent.flags.hasOwnProperty(i)) {
                    this.flags[i] = true;
                }
            }
        }

        var $flags = flag ? flags[flag] : keys(flags)
                , self = this;

        if ($flags) {
            for (var i = 0, l = $flags.length; i < l; i++) {
                // avoid recursion
                if (this.flags[$flags[i]])
                    continue;

                var name = $flags[i]
                        , assertion = new Assertion(this.obj, name, this)

                if ('function' == typeof Assertion.prototype[name]) {
                    // clone the function, make sure we dont touch the prot reference
                    var old = this[name];
                    this[name] = function() {
                        return old.apply(self, arguments);
                    };

                    for (var fn in Assertion.prototype) {
                        if (Assertion.prototype.hasOwnProperty(fn) && fn != name) {
                            this[name][fn] = bind(assertion[fn], assertion);
                        }
                    }
                } else {
                    this[name] = assertion;
                }
            }
        }
    }

    /**
     * Performs an assertion
     *
     * @api private
     */

    Assertion.prototype.assert = function(truth, msg, error, expected) {
        var msg = this.flags.not ? error : msg
                , ok = this.flags.not ? !truth : truth
                , err;

        if (!ok) {
            err = new Error(msg.call(this));
            if (arguments.length > 3) {
                err.actual = this.obj;
                err.expected = expected;
                err.showDiff = true;
            }
            throw err;
        }

        this.and = new Assertion(this.obj);
    };

    /**
     * Check if the value is truthy
     *
     * @api public
     */

    Assertion.prototype.ok = function() {
        this.assert(
                !!this.obj
                , function() {
                    return 'expected ' + i(this.obj) + ' to be truthy'
                }
        , function() {
            return 'expected ' + i(this.obj) + ' to be falsy'
        });
    };

    /**
     * Creates an anonymous function which calls fn with arguments.
     *
     * @api public
     */

    Assertion.prototype.withArgs = function() {
        expect(this.obj).to.be.a('function');
        var fn = this.obj;
        var args = Array.prototype.slice.call(arguments);
        return expect(function() {
            fn.apply(null, args);
        });
    };

    /**
     * Assert that the function throws.
     *
     * @param {Function|RegExp} callback, or regexp to match error string against
     * @api public
     */

    Assertion.prototype.throwError =
            Assertion.prototype.throwException = function(fn) {
                expect(this.obj).to.be.a('function');

                var thrown = false
                        , not = this.flags.not;

                try {
                    this.obj();
                } catch (e) {
                    if (isRegExp(fn)) {
                        var subject = 'string' == typeof e ? e : e.message;
                        if (not) {
                            expect(subject).to.not.match(fn);
                        } else {
                            expect(subject).to.match(fn);
                        }
                    } else if ('function' == typeof fn) {
                        fn(e);
                    }
                    thrown = true;
                }

                if (isRegExp(fn) && not) {
                    // in the presence of a matcher, ensure the `not` only applies to
                    // the matching.
                    this.flags.not = false;
                }

                var name = this.obj.name || 'fn';
                this.assert(
                        thrown
                        , function() {
                            return 'expected ' + name + ' to throw an exception'
                        }
                , function() {
                    return 'expected ' + name + ' not to throw an exception'
                });
            };

    /**
     * Checks if the array is empty.
     *
     * @api public
     */

    Assertion.prototype.empty = function() {
        var expectation;

        if ('object' == typeof this.obj && null !== this.obj && !isArray(this.obj)) {
            if ('number' == typeof this.obj.length) {
                expectation = !this.obj.length;
            } else {
                expectation = !keys(this.obj).length;
            }
        } else {
            if ('string' != typeof this.obj) {
                expect(this.obj).to.be.an('object');
            }

            expect(this.obj).to.have.property('length');
            expectation = !this.obj.length;
        }

        this.assert(
                expectation
                , function() {
                    return 'expected ' + i(this.obj) + ' to be empty'
                }
        , function() {
            return 'expected ' + i(this.obj) + ' to not be empty'
        });
        return this;
    };

    /**
     * Checks if the obj exactly equals another.
     *
     * @api public
     */

    Assertion.prototype.be =
            Assertion.prototype.equal = function(obj) {
                this.assert(
                        obj === this.obj
                        , function() {
                            return 'expected ' + i(this.obj) + ' to equal ' + i(obj)
                        }
                , function() {
                    return 'expected ' + i(this.obj) + ' to not equal ' + i(obj)
                });
                return this;
            };

    /**
     * Checks if the obj sortof equals another.
     *
     * @api public
     */

    Assertion.prototype.eql = function(obj) {
        this.assert(
                expect.eql(this.obj, obj)
                , function() {
                    return 'expected ' + i(this.obj) + ' to sort of equal ' + i(obj)
                }
        , function() {
            return 'expected ' + i(this.obj) + ' to sort of not equal ' + i(obj)
        }
        , obj);
        return this;
    };

    /**
     * Assert within start to finish (inclusive).
     *
     * @param {Number} start
     * @param {Number} finish
     * @api public
     */

    Assertion.prototype.within = function(start, finish) {
        var range = start + '..' + finish;
        this.assert(
                this.obj >= start && this.obj <= finish
                , function() {
                    return 'expected ' + i(this.obj) + ' to be within ' + range
                }
        , function() {
            return 'expected ' + i(this.obj) + ' to not be within ' + range
        });
        return this;
    };

    /**
     * Assert typeof / instance of
     *
     * @api public
     */

    Assertion.prototype.a =
            Assertion.prototype.an = function(type) {
                if ('string' == typeof type) {
                    // proper english in error msg
                    var n = /^[aeiou]/.test(type) ? 'n' : '';

                    // typeof with support for 'array'
                    this.assert(
                            'array' == type ? isArray(this.obj) :
                            'regexp' == type ? isRegExp(this.obj) :
                            'object' == type
                            ? 'object' == typeof this.obj && null !== this.obj
                            : type == typeof this.obj
                            , function() {
                                return 'expected ' + i(this.obj) + ' to be a' + n + ' ' + type
                            }
                    , function() {
                        return 'expected ' + i(this.obj) + ' not to be a' + n + ' ' + type
                    });
                } else {
                    // instanceof
                    var name = type.name || 'supplied constructor';
                    this.assert(
                            this.obj instanceof type
                            , function() {
                                return 'expected ' + i(this.obj) + ' to be an instance of ' + name
                            }
                    , function() {
                        return 'expected ' + i(this.obj) + ' not to be an instance of ' + name
                    });
                }

                return this;
            };

    /**
     * Assert numeric value above _n_.
     *
     * @param {Number} n
     * @api public
     */

    Assertion.prototype.greaterThan =
            Assertion.prototype.above = function(n) {
                this.assert(
                        this.obj > n
                        , function() {
                            return 'expected ' + i(this.obj) + ' to be above ' + n
                        }
                , function() {
                    return 'expected ' + i(this.obj) + ' to be below ' + n
                });
                return this;
            };

    /**
     * Assert numeric value below _n_.
     *
     * @param {Number} n
     * @api public
     */

    Assertion.prototype.lessThan =
            Assertion.prototype.below = function(n) {
                this.assert(
                        this.obj < n
                        , function() {
                            return 'expected ' + i(this.obj) + ' to be below ' + n
                        }
                , function() {
                    return 'expected ' + i(this.obj) + ' to be above ' + n
                });
                return this;
            };

    /**
     * Assert string value matches _regexp_.
     *
     * @param {RegExp} regexp
     * @api public
     */

    Assertion.prototype.match = function(regexp) {
        this.assert(
                regexp.exec(this.obj)
                , function() {
                    return 'expected ' + i(this.obj) + ' to match ' + regexp
                }
        , function() {
            return 'expected ' + i(this.obj) + ' not to match ' + regexp
        });
        return this;
    };

    /**
     * Assert property "length" exists and has value of _n_.
     *
     * @param {Number} n
     * @api public
     */

    Assertion.prototype.length = function(n) {
        expect(this.obj).to.have.property('length');
        var len = this.obj.length;
        this.assert(
                n == len
                , function() {
                    return 'expected ' + i(this.obj) + ' to have a length of ' + n + ' but got ' + len
                }
        , function() {
            return 'expected ' + i(this.obj) + ' to not have a length of ' + len
        });
        return this;
    };

    /**
     * Assert property _name_ exists, with optional _val_.
     *
     * @param {String} name
     * @param {Mixed} val
     * @api public
     */

    Assertion.prototype.property = function(name, val) {
        if (this.flags.own) {
            this.assert(
                    Object.prototype.hasOwnProperty.call(this.obj, name)
                    , function() {
                        return 'expected ' + i(this.obj) + ' to have own property ' + i(name)
                    }
            , function() {
                return 'expected ' + i(this.obj) + ' to not have own property ' + i(name)
            });
            return this;
        }

        if (this.flags.not && undefined !== val) {
            if (undefined === this.obj[name]) {
                throw new Error(i(this.obj) + ' has no property ' + i(name));
            }
        } else {
            var hasProp;
            try {
                hasProp = name in this.obj
            } catch (e) {
                hasProp = undefined !== this.obj[name]
            }

            this.assert(
                    hasProp
                    , function() {
                        return 'expected ' + i(this.obj) + ' to have a property ' + i(name)
                    }
            , function() {
                return 'expected ' + i(this.obj) + ' to not have a property ' + i(name)
            });
        }

        if (undefined !== val) {
            this.assert(
                    val === this.obj[name]
                    , function() {
                        return 'expected ' + i(this.obj) + ' to have a property ' + i(name)
                                + ' of ' + i(val) + ', but got ' + i(this.obj[name])
                    }
            , function() {
                return 'expected ' + i(this.obj) + ' to not have a property ' + i(name)
                        + ' of ' + i(val)
            });
        }

        this.obj = this.obj[name];
        return this;
    };

    /**
     * Assert that the array contains _obj_ or string contains _obj_.
     *
     * @param {Mixed} obj|string
     * @api public
     */

    Assertion.prototype.string =
            Assertion.prototype.contain = function(obj) {
                if ('string' == typeof this.obj) {
                    this.assert(
                            ~this.obj.indexOf(obj)
                            , function() {
                                return 'expected ' + i(this.obj) + ' to contain ' + i(obj)
                            }
                    , function() {
                        return 'expected ' + i(this.obj) + ' to not contain ' + i(obj)
                    });
                } else {
                    this.assert(
                            ~indexOf(this.obj, obj)
                            , function() {
                                return 'expected ' + i(this.obj) + ' to contain ' + i(obj)
                            }
                    , function() {
                        return 'expected ' + i(this.obj) + ' to not contain ' + i(obj)
                    });
                }
                return this;
            };

    /**
     * Assert exact keys or inclusion of keys by using
     * the `.own` modifier.
     *
     * @param {Array|String ...} keys
     * @api public
     */

    Assertion.prototype.key =
            Assertion.prototype.keys = function($keys) {
                var str
                        , ok = true;

                $keys = isArray($keys)
                        ? $keys
                        : Array.prototype.slice.call(arguments);

                if (!$keys.length)
                    throw new Error('keys required');

                var actual = keys(this.obj)
                        , len = $keys.length;

                // Inclusion
                ok = every($keys, function(key) {
                    return ~indexOf(actual, key);
                });

                // Strict
                if (!this.flags.not && this.flags.only) {
                    ok = ok && $keys.length == actual.length;
                }

                // Key string
                if (len > 1) {
                    $keys = map($keys, function(key) {
                        return i(key);
                    });
                    var last = $keys.pop();
                    str = $keys.join(', ') + ', and ' + last;
                } else {
                    str = i($keys[0]);
                }

                // Form
                str = (len > 1 ? 'keys ' : 'key ') + str;

                // Have / include
                str = (!this.flags.only ? 'include ' : 'only have ') + str;

                // Assertion
                this.assert(
                        ok
                        , function() {
                            return 'expected ' + i(this.obj) + ' to ' + str
                        }
                , function() {
                    return 'expected ' + i(this.obj) + ' to not ' + str
                });

                return this;
            };

    /**
     * Assert a failure.
     *
     * @param {String ...} custom message
     * @api public
     */
    Assertion.prototype.fail = function(msg) {
        var error = function() {
            return msg || "explicit failure";
        }
        this.assert(false, error, error);
        return this;
    };

    /**
     * Function bind implementation.
     */

    function bind(fn, scope) {
        return function() {
            return fn.apply(scope, arguments);
        }
    }

    /**
     * Array every compatibility
     *
     * @see bit.ly/5Fq1N2
     * @api public
     */

    function every(arr, fn, thisObj) {
        var scope = thisObj || global;
        for (var i = 0, j = arr.length; i < j; ++i) {
            if (!fn.call(scope, arr[i], i, arr)) {
                return false;
            }
        }
        return true;
    }

    /**
     * Array indexOf compatibility.
     *
     * @see bit.ly/a5Dxa2
     * @api public
     */

    function indexOf(arr, o, i) {
        if (Array.prototype.indexOf) {
            return Array.prototype.indexOf.call(arr, o, i);
        }

        if (arr.length === undefined) {
            return -1;
        }

        for (var j = arr.length, i = i < 0 ? i + j < 0 ? 0 : i + j : i || 0
                ; i < j && arr[i] !== o; i++)
            ;

        return j <= i ? -1 : i;
    }

    // https://gist.github.com/1044128/
    var getOuterHTML = function(element) {
        if ('outerHTML' in element)
            return element.outerHTML;
        var ns = "http://www.w3.org/1999/xhtml";
        var container = document.createElementNS(ns, '_');
        var xmlSerializer = new XMLSerializer();
        var html;
        if (document.xmlVersion) {
            return xmlSerializer.serializeToString(element);
        } else {
            container.appendChild(element.cloneNode(false));
            html = container.innerHTML.replace('><', '>' + element.innerHTML + '<');
            container.innerHTML = '';
            return html;
        }
    };

    // Returns true if object is a DOM element.
    var isDOMElement = function(object) {
        if (typeof HTMLElement === 'object') {
            return object instanceof HTMLElement;
        } else {
            return object &&
                    typeof object === 'object' &&
                    object.nodeType === 1 &&
                    typeof object.nodeName === 'string';
        }
    };

    /**
     * Inspects an object.
     *
     * @see taken from node.js `util` module (copyright Joyent, MIT license)
     * @api private
     */

    function i(obj, showHidden, depth) {
        var seen = [];

        function stylize(str) {
            return str;
        }

        function format(value, recurseTimes) {
            // Provide a hook for user-specified inspect functions.
            // Check that value is an object with an inspect function on it
            if (value && typeof value.inspect === 'function' &&
                    // Filter out the util module, it's inspect function is special
                    value !== exports &&
                    // Also filter out any prototype objects using the circular check.
                    !(value.constructor && value.constructor.prototype === value)) {
                return value.inspect(recurseTimes);
            }

            // Primitive types cannot have properties
            switch (typeof value) {
                case 'undefined':
                    return stylize('undefined', 'undefined');

                case 'string':
                    var simple = '\'' + json.stringify(value).replace(/^"|"$/g, '')
                            .replace(/'/g, "\\'")
                            .replace(/\\"/g, '"') + '\'';
                    return stylize(simple, 'string');

                case 'number':
                    return stylize('' + value, 'number');

                case 'boolean':
                    return stylize('' + value, 'boolean');
            }
            // For some reason typeof null is "object", so special case here.
            if (value === null) {
                return stylize('null', 'null');
            }

            if (isDOMElement(value)) {
                return getOuterHTML(value);
            }

            // Look up the keys of the object.
            var visible_keys = keys(value);
            var $keys = showHidden ? Object.getOwnPropertyNames(value) : visible_keys;

            // Functions without properties can be shortcutted.
            if (typeof value === 'function' && $keys.length === 0) {
                if (isRegExp(value)) {
                    return stylize('' + value, 'regexp');
                } else {
                    var name = value.name ? ': ' + value.name : '';
                    return stylize('[Function' + name + ']', 'special');
                }
            }

            // Dates without properties can be shortcutted
            if (isDate(value) && $keys.length === 0) {
                return stylize(value.toUTCString(), 'date');
            }

            // Error objects can be shortcutted
            if (value instanceof Error) {
                return stylize("[" + value.toString() + "]", 'Error');
            }

            var base, type, braces;
            // Determine the object type
            if (isArray(value)) {
                type = 'Array';
                braces = ['[', ']'];
            } else {
                type = 'Object';
                braces = ['{', '}'];
            }

            // Make functions say that they are functions
            if (typeof value === 'function') {
                var n = value.name ? ': ' + value.name : '';
                base = (isRegExp(value)) ? ' ' + value : ' [Function' + n + ']';
            } else {
                base = '';
            }

            // Make dates with properties first say the date
            if (isDate(value)) {
                base = ' ' + value.toUTCString();
            }

            if ($keys.length === 0) {
                return braces[0] + base + braces[1];
            }

            if (recurseTimes < 0) {
                if (isRegExp(value)) {
                    return stylize('' + value, 'regexp');
                } else {
                    return stylize('[Object]', 'special');
                }
            }

            seen.push(value);

            var output = map($keys, function(key) {
                var name, str;
                if (value.__lookupGetter__) {
                    if (value.__lookupGetter__(key)) {
                        if (value.__lookupSetter__(key)) {
                            str = stylize('[Getter/Setter]', 'special');
                        } else {
                            str = stylize('[Getter]', 'special');
                        }
                    } else {
                        if (value.__lookupSetter__(key)) {
                            str = stylize('[Setter]', 'special');
                        }
                    }
                }
                if (indexOf(visible_keys, key) < 0) {
                    name = '[' + key + ']';
                }
                if (!str) {
                    if (indexOf(seen, value[key]) < 0) {
                        if (recurseTimes === null) {
                            str = format(value[key]);
                        } else {
                            str = format(value[key], recurseTimes - 1);
                        }
                        if (str.indexOf('\n') > -1) {
                            if (isArray(value)) {
                                str = map(str.split('\n'), function(line) {
                                    return '  ' + line;
                                }).join('\n').substr(2);
                            } else {
                                str = '\n' + map(str.split('\n'), function(line) {
                                    return '   ' + line;
                                }).join('\n');
                            }
                        }
                    } else {
                        str = stylize('[Circular]', 'special');
                    }
                }
                if (typeof name === 'undefined') {
                    if (type === 'Array' && key.match(/^\d+$/)) {
                        return str;
                    }
                    try {
                        name = json.stringify('' + key);
                    } catch (e) {
                        alert("ddd")
                    }
                    if (name.match(/^"([a-zA-Z_][a-zA-Z_0-9]*)"$/)) {
                        name = name.substr(1, name.length - 2);
                        name = stylize(name, 'name');
                    } else {
                        name = name.replace(/'/g, "\\'")
                                .replace(/\\"/g, '"')
                                .replace(/(^"|"$)/g, "'");
                        name = stylize(name, 'string');
                    }
                }

                return name + ': ' + str;
            });

            seen.pop();

            var numLinesEst = 0;
            var length = reduce(output, function(prev, cur) {
                numLinesEst++;
                if (indexOf(cur, '\n') >= 0)
                    numLinesEst++;
                return prev + cur.length + 1;
            }, 0);

            if (length > 50) {
                output = braces[0] +
                        (base === '' ? '' : base + '\n ') +
                        ' ' +
                        output.join(',\n  ') +
                        ' ' +
                        braces[1];

            } else {
                output = braces[0] + base + ' ' + output.join(', ') + ' ' + braces[1];
            }

            return output;
        }
        return format(obj, (typeof depth === 'undefined' ? 2 : depth));
    }

    expect.stringify = i;

    function isArray(ar) {
        return Object.prototype.toString.call(ar) === '[object Array]';
    }

    function isRegExp(re) {
        var s;
        try {
            s = '' + re;
        } catch (e) {
            return false;
        }

        return re instanceof RegExp || // easy case
                // duck-type for context-switching evalcx case
                typeof (re) === 'function' &&
                re.constructor.name === 'RegExp' &&
                re.compile &&
                re.test &&
                re.exec &&
                s.match(/^\/.*\/[gim]{0,3}$/);
    }

    function isDate(d) {
        return d instanceof Date;
    }

    function keys(obj) {
        if ( /\[native code\]/.test(Object.keys)) {
            return Object.keys(obj);
        }

        var keys = [];

        for (var i in obj) {
            if (Object.prototype.hasOwnProperty.call(obj, i)) {
                keys.push(i);
            }
        }

        return keys;
    }

    function map(arr, mapper, that) {
        if (Array.prototype.map) {
            return Array.prototype.map.call(arr, mapper, that);
        }

        var other = new Array(arr.length);

        for (var i = 0, n = arr.length; i < n; i++)
            if (i in arr)
                other[i] = mapper.call(that, arr[i], i, arr);

        return other;
    }

    function reduce(arr, fun) {
        if (Array.prototype.reduce) {
            return Array.prototype.reduce.apply(
                    arr
                    , Array.prototype.slice.call(arguments, 1)
                    );
        }

        var len = +this.length;

        if (typeof fun !== "function")
            throw new TypeError();

        // no value to return if no initial value and an empty array
        if (len === 0 && arguments.length === 1)
            throw new TypeError();

        var i = 0;
        if (arguments.length >= 2) {
            var rv = arguments[1];
        } else {
            do {
                if (i in this) {
                    rv = this[i++];
                    break;
                }

                // if array contains no values, no initial value to return
                if (++i >= len)
                    throw new TypeError();
            } while (true);
        }

        for (; i < len; i++) {
            if (i in this)
                rv = fun.call(null, rv, this[i], i, this);
        }

        return rv;
    }

    /**
     * Asserts deep equality
     *
     * @see taken from node.js `assert` module (copyright Joyent, MIT license)
     * @api private
     */

    expect.eql = function eql(actual, expected) {
        // 7.1. All identical values are equivalent, as determined by ===.
        if (actual === expected) {
            return true;
        } else if ('undefined' != typeof Buffer
                && Buffer.isBuffer(actual) && Buffer.isBuffer(expected)) {
            if (actual.length != expected.length)
                return false;

            for (var i = 0; i < actual.length; i++) {
                if (actual[i] !== expected[i])
                    return false;
            }

            return true;

            // 7.2. If the expected value is a Date object, the actual value is
            // equivalent if it is also a Date object that refers to the same time.
        } else if (actual instanceof Date && expected instanceof Date) {
            return actual.getTime() === expected.getTime();

            // 7.3. Other pairs that do not both pass typeof value == "object",
            // equivalence is determined by ==.
        } else if (typeof actual != 'object' && typeof expected != 'object') {
            return actual == expected;
            // If both are regular expression use the special `regExpEquiv` method
            // to determine equivalence.
        } else if (isRegExp(actual) && isRegExp(expected)) {
            return regExpEquiv(actual, expected);
            // 7.4. For all other Object pairs, including Array objects, equivalence is
            // determined by having the same number of owned properties (as verified
            // with Object.prototype.hasOwnProperty.call), the same set of keys
            // (although not necessarily the same order), equivalent values for every
            // corresponding key, and an identical "prototype" property. Note: this
            // accounts for both named and indexed properties on Arrays.
        } else {
            return objEquiv(actual, expected);
        }
    };

    function isUndefinedOrNull(value) {
        return value === null || value === undefined;
    }

    function isArguments(object) {
        return Object.prototype.toString.call(object) == '[object Arguments]';
    }

    function regExpEquiv(a, b) {
        return a.source === b.source && a.global === b.global &&
                a.ignoreCase === b.ignoreCase && a.multiline === b.multiline;
    }

    function objEquiv(a, b) {
        if (isUndefinedOrNull(a) || isUndefinedOrNull(b))
            return false;
        // an identical "prototype" property.
        if (a.prototype !== b.prototype)
            return false;
        //~~~I've managed to break Object.keys through screwy arguments passing.
        //   Converting to array solves the problem.
        if (isArguments(a)) {
            if (!isArguments(b)) {
                return false;
            }
            a = pSlice.call(a);
            b = pSlice.call(b);
            return expect.eql(a, b);
        }
        try {
            var ka = keys(a),
                    kb = keys(b),
                    key, i;
        } catch (e) {//happens when one is a string literal and the other isn't
            return false;
        }
        // having the same number of owned properties (keys incorporates hasOwnProperty)
        if (ka.length != kb.length)
            return false;
        //the same set of keys (although not necessarily the same order),
        ka.sort();
        kb.sort();
        //~~~cheap key test
        for (i = ka.length - 1; i >= 0; i--) {
            if (ka[i] != kb[i])
                return false;
        }
        //equivalent values for every corresponding key, and
        //~~~possibly expensive deep test
        for (i = ka.length - 1; i >= 0; i--) {
            key = ka[i];
            if (!expect.eql(a[key], b[key]))
                return false;
        }
        return true;
    }

    var json = (function() {
        "use strict";

        if ('object' == typeof JSON && JSON.parse && JSON.stringify) {
            return {
                parse: nativeJSON.parse
                , stringify: nativeJSON.stringify
            }
        }

        var JSON = {};

        function f(n) {
            // Format integers to have at least two digits.
            return n < 10 ? '0' + n : n;
        }

        function date(d, key) {
            return isFinite(d.valueOf()) ?
                    d.getUTCFullYear() + '-' +
                    f(d.getUTCMonth() + 1) + '-' +
                    f(d.getUTCDate()) + 'T' +
                    f(d.getUTCHours()) + ':' +
                    f(d.getUTCMinutes()) + ':' +
                    f(d.getUTCSeconds()) + 'Z' : null;
        }

        var cx = /[\u0000\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,
                escapable = /[\\\"\x00-\x1f\x7f-\x9f\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,
                gap,
                indent,
                meta = {// table of character substitutions
                    '\b': '\\b',
                    '\t': '\\t',
                    '\n': '\\n',
                    '\f': '\\f',
                    '\r': '\\r',
                    '"': '\\"',
                    '\\': '\\\\'
                },
        rep;


        function quote(string) {

            // If the string contains no control characters, no quote characters, and no
            // backslash characters, then we can safely slap some quotes around it.
            // Otherwise we must also replace the offending characters with safe escape
            // sequences.

            escapable.lastIndex = 0;
            return escapable.test(string) ? '"' + string.replace(escapable, function(a) {
                var c = meta[a];
                return typeof c === 'string' ? c :
                        '\\u' + ('0000' + a.charCodeAt(0).toString(16)).slice(-4);
            }) + '"' : '"' + string + '"';
        }


        function str(key, holder) {

            // Produce a string from holder[key].

            var i, // The loop counter.
                    k, // The member key.
                    v, // The member value.
                    length,
                    mind = gap,
                    partial,
                    value = holder[key];

            // If the value has a toJSON method, call it to obtain a replacement value.

            if (value instanceof Date) {
                value = date(key);
            }

            // If we were called with a replacer function, then call the replacer to
            // obtain a replacement value.

            if (typeof rep === 'function') {
                value = rep.call(holder, key, value);
            }

            // What happens next depends on the value's type.

            switch (typeof value) {
                case 'string':
                    return quote(value);

                case 'number':

                    // JSON numbers must be finite. Encode non-finite numbers as null.

                    return isFinite(value) ? String(value) : 'null';

                case 'boolean':
                case 'null':

                    // If the value is a boolean or null, convert it to a string. Note:
                    // typeof null does not produce 'null'. The case is included here in
                    // the remote chance that this gets fixed someday.

                    return String(value);

                    // If the type is 'object', we might be dealing with an object or an array or
                    // null.

                case 'object':

                    // Due to a specification blunder in ECMAScript, typeof null is 'object',
                    // so watch out for that case.

                    if (!value) {
                        return 'null';
                    }

                    // Make an array to hold the partial results of stringifying this object value.

                    gap += indent;
                    partial = [];

                    // Is the value an array?

                    if (Object.prototype.toString.apply(value) === '[object Array]') {

                        // The value is an array. Stringify every element. Use null as a placeholder
                        // for non-JSON values.

                        length = value.length;
                        for (i = 0; i < length; i += 1) {
                            partial[i] = str(i, value) || 'null';
                        }

                        // Join all of the elements together, separated with commas, and wrap them in
                        // brackets.

                        v = partial.length === 0 ? '[]' : gap ?
                                '[\n' + gap + partial.join(',\n' + gap) + '\n' + mind + ']' :
                                '[' + partial.join(',') + ']';
                        gap = mind;
                        return v;
                    }

                    // If the replacer is an array, use it to select the members to be stringified.

                    if (rep && typeof rep === 'object') {
                        length = rep.length;
                        for (i = 0; i < length; i += 1) {
                            if (typeof rep[i] === 'string') {
                                k = rep[i];
                                v = str(k, value);
                                if (v) {
                                    partial.push(quote(k) + (gap ? ': ' : ':') + v);
                                }
                            }
                        }
                    } else {

                        // Otherwise, iterate through all of the keys in the object.

                        for (k in value) {
                            if (Object.prototype.hasOwnProperty.call(value, k)) {
                                v = str(k, value);
                                if (v) {
                                    partial.push(quote(k) + (gap ? ': ' : ':') + v);
                                }
                            }
                        }
                    }

                    // Join all of the member texts together, separated with commas,
                    // and wrap them in braces.

                    v = partial.length === 0 ? '{}' : gap ?
                            '{\n' + gap + partial.join(',\n' + gap) + '\n' + mind + '}' :
                            '{' + partial.join(',') + '}';
                    gap = mind;
                    return v;
            }
        }

        // If the JSON object does not yet have a stringify method, give it one.

        JSON.stringify = function(value, replacer, space) {

            // The stringify method takes a value and an optional replacer, and an optional
            // space parameter, and returns a JSON text. The replacer can be a function
            // that can replace values, or an array of strings that will select the keys.
            // A default replacer method can be provided. Use of the space parameter can
            // produce text that is more easily readable.

            var i;
            gap = '';
            indent = '';

            // If the space parameter is a number, make an indent string containing that
            // many spaces.

            if (typeof space === 'number') {
                for (i = 0; i < space; i += 1) {
                    indent += ' ';
                }

                // If the space parameter is a string, it will be used as the indent string.

            } else if (typeof space === 'string') {
                indent = space;
            }

            // If there is a replacer, it must be a function or an array.
            // Otherwise, throw an error.

            rep = replacer;
            if (replacer && typeof replacer !== 'function' &&
                    (typeof replacer !== 'object' ||
                            typeof replacer.length !== 'number')) {
                throw new Error('JSON.stringify');
            }

            // Make a fake root object containing our value under the key of ''.
            // Return the result of stringifying the value.

            return str('', {'': value});
        };

        // If the JSON object does not yet have a parse method, give it one.

        JSON.parse = function(text, reviver) {
            // The parse method takes a text and an optional reviver function, and returns
            // a JavaScript value if the text is a valid JSON text.

            var j;

            function walk(holder, key) {

                // The walk method is used to recursively walk the resulting structure so
                // that modifications can be made.

                var k, v, value = holder[key];
                if (value && typeof value === 'object') {
                    for (k in value) {
                        if (Object.prototype.hasOwnProperty.call(value, k)) {
                            v = walk(value, k);
                            if (v !== undefined) {
                                value[k] = v;
                            } else {
                                delete value[k];
                            }
                        }
                    }
                }
                return reviver.call(holder, key, value);
            }


            // Parsing happens in four stages. In the first stage, we replace certain
            // Unicode characters with escape sequences. JavaScript handles many characters
            // incorrectly, either silently deleting them, or treating them as line endings.

            text = String(text);
            cx.lastIndex = 0;
            if (cx.test(text)) {
                text = text.replace(cx, function(a) {
                    return '\\u' +
                            ('0000' + a.charCodeAt(0).toString(16)).slice(-4);
                });
            }

            // In the second stage, we run the text against regular expressions that look
            // for non-JSON patterns. We are especially concerned with '()' and 'new'
            // because they can cause invocation, and '=' because it can cause mutation.
            // But just to be safe, we want to reject all unexpected forms.

            // We split the second stage into 4 regexp operations in order to work around
            // crippling inefficiencies in IE's and Safari's regexp engines. First we
            // replace the JSON backslash pairs with '@' (a non-JSON character). Second, we
            // replace all simple value tokens with ']' characters. Third, we delete all
            // open brackets that follow a colon or comma or that begin the text. Finally,
            // we look to see that the remaining characters are only whitespace or ']' or
            // ',' or ':' or '{' or '}'. If that is so, then the text is safe for eval.

            if (/^[\],:{}\s]*$/
                    .test(text.replace(/\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g, '@')
                            .replace(/"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g, ']')
                            .replace(/(?:^|:|,)(?:\s*\[)+/g, ''))) {

                // In the third stage we use the eval function to compile the text into a
                // JavaScript structure. The '{' operator is subject to a syntactic ambiguity
                // in JavaScript: it can begin a block or an object literal. We wrap the text
                // in parens to eliminate the ambiguity.

                j = eval('(' + text + ')');

                // In the optional fourth stage, we recursively walk the new structure, passing
                // each name/value pair to a reviver function for possible transformation.

                return typeof reviver === 'function' ?
                        walk({'': j}, '') : j;
            }

            // If the text is not JSON parseable, then a SyntaxError is thrown.

            throw new SyntaxError('JSON.parse');
        };

        return JSON;
    })();

    if ('undefined' != typeof window) {
        window.expect = module.exports;
    }

})(
        this
        , 'undefined' != typeof module ? module : {exports: {}}
);